Model 8901B Service
8-9.
POWER-UP
CHECKS
When the Modulation Analyzer is first turned on
(or
if
40.0
SPCL is entered), the instrument goes
through
a
series of operational checks. If a check fails, an error code is displayed for
two
seconds on
the four internal TEST LEDs on the A13 Controller Assembly. The sequence then continues on
to
the
next check.
Except for the check of the front-panel LED annunciators, no indication of the power-up sequence
or
its results is given on the front-panel display. The principal advantage
to
using the Power-Up Checks
is
that the keyboard and display need not be operational.
To use the Power-Up Checks, remove the top cover, remove any jumpers that may be on the four TEST
test points
(A,
B, C, and D) on the A13 Controller Assembly, remove any signal at the INPUT and
switch POWER
to
STBY for five seconds (to discharge the supplies) and back
to
ON. Observe the four
TEST
LEDs on the top of the Controller Assembly as the instrument powers up. The LEDs should
light in the following sequence:
1.
Indeterminate for about second.
2.
(
)(
)(
)(1)
for about 2 seconds.
3.
(
)(
)(2)(
)
for about
1/4
second.
4.
(
)(4)(
)(
)
for about
second.
5.
(8)(4)(2)(1) for about
10
seconds.
6.
( )( )(
)(1), with
(1)
blinking indefinitely until a key is pressed.
The Power-Up Checks proper begin at
step
2
and are carried out in the following order:
1.
Front-Panel Annunciator Check.
All front-panel LEDs and display segments and decimal points
are lighted and remain
so
throughout the tests that follow and for a few seconds afterwards. Failure
of one
or
more LEDs
or
display segments to light indicates that the respective components or
drive circuits have failed. See Service Sheets 26 and
27.
2.
Read Only Memory Check.
The checksum of each of the read only memories
(ROMs)
is read
and compared against
a
stored reference (stored in ROM
1).
This
is
similar
to
issuing a series of
52.N SPCL commands (see
Service Special finctions,
paragraph
8-7).
When a wrong checksum
is
found, the four TEST LEDs blink for one second with the binary code of the ROM number.
For
example,
if
ROM
3
is faulty, the
TEST
LEDs will blink
(
)(
)(2)(1)
(that is, a binary
3).
The
check then continues on to the next ROM. See Service Sheets BD5 and
24.
If no faulty ROM
is
found, a steady
(
)(
)(
)(1)
appears for about
2
seconds.
3.
Random Access Memory Check.
Data
is
written into and retrieved from the random access
memory (RAM). During the test,
(
)(
)(2)(
)
is output
to
the
TEST
LEDs for about
2
seconds. If
the
data
read back differs from the data entered, the failure is indicated by outputting the same
code for an additional
2
seconds. See Service Sheet
24.
4.
Instrument Bus Parity Check.
A
parity check of the
data
lines of the Instrument Bus is made.
A
failure is indicated by
(
)(
)(2)(1) on the TEST LEDs for about
2
seconds. See Service Sheets
BD5, 15, and 24.
5.
Local Oscillator Check.
The Local Oscillator
(LO)
is given a series of tests similar to issuing the
54.0
SPCL command (see
Service Special Rmctions,
paragraph
8-7).
During the test,
(
)(4)(
)(
)
is
output
to
the TEST LEDs for about second.
A
failure is indicated by outputting the same
code for an additional 2 seconds. See Service Sheet BD2.
6.
Keyboard Check.
The keyboard is scanned to see
if
any keys are down.
If
a key
is
down, error
code
(
)(4)(
)(1)
is output to the TEST LEDs for
2
seconds. See Service Sheets BD5 and
25.
Power-Up Checks
8B-17
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